You're considering only zigzagoon, not the team as a whole.
There are four Pokemon who can do what I'm thinking. What I'm thinking is Memento
They are Koffing, grimer, ralts and duskull. I think you know it's effects but I'll tell it again.
Lowers the target's Attack and Special Attack by 2 stages. The user faints. This move does not check accuracy, and can hit targets in the middle of a two-turn move. Fails entirely if the target's Attack and Special Attack stat stages are both -6.
some of them have charm, while others have major status affecting moves like willo-wisp, toxic etc.
Then I believe zigzagoon comes in, belly drums and drinks berry juice while opponent switches. Then, needless to say, zigzagoon sweeps with e speed if no ghost types and zigy of course carries more than 2 moves. I hope you get what I meant.
2nd reason can be late game cleaning. Like e killer in ubers, it can do great late game cleaning with belly drum. Remember then, there was no team preview. So trainers couldn't know what's left in their opponent's pocket. They can give bad ziggy's check unknowingly. I believe all these factors led to it's ban.
EDIT: spelling edits
Hope I Helped!